There are two levels of ADMINISTRATOR accounts on non-managed computers. To enable the higher level ADMINSTRATOR , right click on COMPUTER on the START menu and then select MANAGE. Under SYSTEM & TOOLS select LOCAL USERS & GROUPS then select USERS. You will see a list of everyone including all those with the lower level ADMINISTRATOR privileges. Right click on the higher level ADMINISTRATOR and under PROPERTIES then UNSELECT the ACCOUNT IS DISABLED.

Of course you have to know the password. Try the standards if you never set it (ADMIN, admin, password, PASSWORD, etc.). Once you log into this account you can do anything. I strongly recommend against changing this password.